Tips for proper topology
This a fairly large topic. But i try to give a rough overview that may serve as a general guideline for further investigation.

Main goals of good topology:


Animation friendly mesh
Being as low poly as possible


Why animation friendly:

In real world skin behaves like a tight layer that gets stretched by the muscles and bones right beneath it. Logically real skin does not have any polygons, meaning it bends right where the muscle is.
But in 3D we have polygons and this is a problem. Mesh deforms along the edge loops. If the edge loops and the desired wrinkles are not exactly at the same position, the mesh will deform not correctly, exposing the faces and creating artifacts.

Firt pragmatical fix, most of the people come up with "just increase the polycount until i see no more artifacts. But this is NOT how you do it. You want to keep your polycount as low as possible!

Why low poly:

Many inexperienced people think, their mesh only gets professional if it has a high polycount. But the opposite is the case! You need to keep your polycount low at all costs. Otherwise editing your mesh gets needlessly tedious. Also skinning (=weight painting the mesh to bones) your mesh gets more tricky. Not to mention it simply costs more compute power.

How to achieve animation friendly topology:

In general your mesh must follow roughly the form of the muscles and wrinkles of your model.

This means you have to look, where the muscles are and where they push the skin and where the skin forms wrinkles. Then try to build edge loops along those positions.

The face is especially tricky because there are lots of muscles at the same spot. Logically you can't rebuild all of them, because of "being low poly". So you have to find a good balance between those two rules. Mainly it depends on what amount of realism you are going for. If it is anime or toon style, you can ignore most of the muscles and just priorize the wrinkles of the skin. But if you are going for non stylized, pure realism, you have to study the human body and try to recreate most of the muscles in your topology.

Most important wrinkles of the head:


Eyes
Mouth
Nose
Jaw


If those parts don't have an edge loop, your head will most likely don't deform well.

How to achieve low poly:

Only set an edge loop where it is necessary! If the edge loop does not add anything to the mesh's detail, delete it. Use support edges wisely and with caution. 

Where is the line between high and low poly:

Generally everything you model by hand, is still considered low poly. Modeling the mere foundation of wrinkles/creases is the highest form of low poly. If you are defining a complete shaped and sharp crease you are most likely already over the top of low poly.

Such fine details aswell as pores or mini wrinkles (like finger wrinkles) are not part of low poly and will be added using a normal and/or displacement map!

I created a pinterest side for some examples of good topology: https://de.pinterest.com/demons_fate/mesh-toplogy/